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LONDON — The longest study yet on prostate cancer testing provides more evidence that getting screened doesn't cut the chances of dying from the disease.

In a 20-year study of more than 9,000 Swedish men, researchers found no difference in the rate of prostate cancer deaths between the men who were periodically screened and those who weren't.

Routine screening for prostate cancer is controversial and the new results aren't likely to end the debate about the value of testing. Critics say screening leads to unnecessary biopsies and treatment with little proof that it saves lives. Testing is done with a physical exam and a PSA blood test.

"There is no escaping the fact that we need a better tool ... to help detect prostate cancers that actually need treating, as opposed to innocent ones that do not," said Malcolm Mason, a prostate cancer expert at Cancer Research U.K. in a statement. "In the meantime, men should be fully informed about the pros and cons of having their PSA measured."

The standard PSA blood test looks for high levels of prostate specific antigen. The test is controversial because the PSA level can be high for many reasons. A positive result must be confirmed by a biopsy.

If prostate cancer is found, there's no agreement on the best way to treat it: "watchful waiting," surgery, hormone therapy, radiation, or some combination of those. Most tumors grow so slowly they are never life-threatening, and the treatments can have serious side effects.

The Swedish study was done in the eastern Sweden city of Norrkoping. From 9,026 men, about 1,500 were randomly selected to be screened every three years from 1987 to 1996. They only got digital exams on the first two visits; the PSA test was added for the next two. For the fourth and final screening, only men aged 69 or under were included. The remaining 7,532 men were not screened.

During the 20 years of follow-up, 85 men (about 6 percent) in the screened group and 292 men (about 4 percent) in the no-screening group were diagnosed with prostate cancer. The death rate from prostate cancer was similar in both groups, the researchers reported.

The tumors found in the men who got tested were smaller and mostly hadn't spread compared to the tumors found in the other group.

"Screening for prostate cancer did not seem to have a significant effect on mortality," wrote Gabriel Sandblom of the Karolinska Institute in Sweden and colleagues.

The study was paid for by the Swedish Cancer Foundation and other groups. It was published online Thursday in the journal, BMJ.

The American Cancer Society does not recommend routine screening for most men and there is no government screening program in Britain because officials say the PSA test is too unreliable. Two other big papers published in recent years have also failed to show much benefit for screening. That includes a large European study that found screening for prostate cancer could pick up cases a decade earlier, but to prevent one death from cancer, 1,410 men would have to be tested and 48 men treated.

False positive tests can cause significant harms, including psychological distress and treatments that can cause impotence and incontinence.